I found this program on RTL where a reporter takes a look on how people in Luxembourg think about the wedding and what kind of souvenirs there are to buy: RTL.lu - RTL Replay I liked the idea of the wall where people could write their congratulations to the couple.

Family of the Duke:
HHKKKKHH Archduke Christian and Archduchess Marie-Astrid of Austria
HSH Prince Nicolas and HRH Princess Margaretha of Liechtenstein
HRH Prince Jean of Luxembourg and Duchess Diane de Nassau
HHKKHH Prince Guillaume and Princess Sibilla of Luxembourg

Members of the Grand Ducal family and De Lannoy:
Mr. and Mrs. Luis Mestre
Ms. Catalina Esteve
Mr. Antonio Mestre
Ms. Hélène Vestur
Count de Lannoy
Count Jehan de Lannoy
The Count and Countess de Lannoy Christian
Mr. and Mrs. John Hamilton
Miss Antonia Hamilton
Gaëlle Countess de Lannoy
Count Amaury de Lannoy
The Count and Countess Olivier de Lannoy
Mr. and Mrs. Jean-Charles de le Court
Countess Albert de Lannoy
Countess Isabelle de Lannoy
The Count and the Countess Claude de Lannoy
Mr. and Mrs. Ladislas della Faille the Leverghem
The Knight and Mrs. Dominique de Schaetzen
Mr. and Mrs. Dominique della Faille the Lerverghem
Mr. and Mrs. Arnaud della Faille the Lerverghem

Members of Foreign Royal Families:
HRH Princess Lalla Salma of Morocco
HHMM the King and Queen of the Belgians
HHMM the King and Queen of Norway
HHDDHH the Prince Regent and Princess of Liechtenstein
HM the Queen of the Netherlands
HM The Queen of Sweden
HM the Queen of Denmark and HRH the Prince Consort,
HHKKHH Crown Prince Frederik and Crown Princess Mary of Denmark
HHKKHH Crown Princess Victoria and Prince Daniel of Sweden
HHKKHH the Prince and Princess of Asturias
HHKKHH the Prince of Orange and Princess Máxima of the Netherlands
HRH the Crown Prince of Japan
HHKKHH Crown Prince Haakon and Crown Princess Mette-Marit of Norway
HHKKHH the Duke and Duchess of Brabant
HRH Princess Märtha Louise of Norway and Mr. Ari Behn
HRH Prince Carl Philip of Sweden
HHKKHH Prince Laurent and Princess Claire of Belgium
HHKKHH Princess Astrid and Prince Lorenz of Belgium
HHKKHH Prince Rashid and Princess Zeina of Jordan
HHKKHH the Crown Princess and Prince Radu of Romania
HRH the Princess of Hanover
HHKKHH Prince Hassan of Jordan and Princess Sarvath
HHKKHH Prince and Princess Edward of Wessex
HHMM King Constantine and Queen Anne-Marie of Greece
HHMM the King and Queen of Bulgaria

Source Place Royale (according the webiste the list was provided by the Luxembourg court today)
Translated with google translate)

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